Metallized plastics have become of interest in recent years as a replacement for metal in such articles as automobiles, enclosures for electrical appliances, microwave ovens, business machines and the like. When fabricated of plastics alone, such articles are inadequate to shield internal parts from external radiation sources. Also, plastic articles often need a metallized exterior coating for an aesthetic appearance. The metal coatings are provided on the surface of the plastic substrate typically by electroless or electrolytic deposition.
A plastic product sold commercially by General Electric Company under the tradename NORYL.RTM. is often used in applications requiring a metal coating on the exterior surface. Noryl products are commercially available mainly as mixtures of polyphenylene ether (PPE) with poly(alkenylaromatic compounds), also sometimes referred to as polystyrene (PS).
One of the most serious problems which arise in the metallization of plastics is the lack of adhesion of the metal layer to the plastic substrate. One principal method for improving adhesion of metal layers to the substrate surfaces of polyphenylene ether and polystyrene mixtures involves surface treatment with chromic acid to provide crevices in the substrate surface for the subsequent metal coating to adhere to.
In order to produce crevices on a substrate surface, such as Noryl, which in turn promotes adhesion when metal is later deposited, the surface of the Noryl has to be created such that the etching solution, (i.e., chromic acid), can selectively etch a particular component in the substrate composition. Presently, a plating grade of Noryl PN235 employs a large quantity of rubber in the blend, so that the etching solution can attack the rubber preferentially. However, high rubber content in the Noryl PN235 composition, also causes the heat distortion temperature (HDT) of the substrate to decrease. In exterior applications, such as automotive wheel covers, enhanced heat performance is required. Thus, to maintain the heat distortion temperature or enhance the heat performance, there is a need for an improved platable Noryl composition having high heat properties and good adhesion with metallic coatings. Such compositions and method are provided by the present invention.